Prediction and Evaluation of Li2ZnS2 Crystals as Mid-Infrared Nonlinear Optical Material with High Thermal Conductivity

Infrared (IR) nonlinear optical (NLO) crystals are essential for laser applications in mid- or far-IR regions. The common mid-IR NLO crystals are inadequate under high-power laser mainly due to low laser-induced damage threshold which is closely related to the lattice thermal conductivity (kappa L). Here a combined method involving automatic structure prediction algorithms, first-principles calculations and machine learning model is used to predict and evaluate a new IR NLO material family with the chemical formula of Li2ZnS2. Totally, three Li2ZnS2 structures (or phases) are designed, where one phase is expected to meet the stringent requirements for mid-IR NLO materials pumped by high-power laser, with the high thermal conductivity, decent NLO coefficient, wide bandgap and phase-matching ability in the mid-IR region. This study presents an efficient approach to exploring mid-IR NLO materials with high kappa L based on accumulated knowledge concerning the structure-property relationship in the NLO field and provides inspiration to improve kappa L prediction.